Require output fixture extension to match sourceType output.

packages/babel-plugin-transform-function-name/test/fixtures/function-name/export/output.mjs

@@ -0,0 +1,22 @@
+var _foo = "yes",
+    foob = "no";
+export { _foo as foo, foob };
+
+function _whatever() {}
+
+export { _whatever as whatever };
+
+function _wowzers() {}
+
+export { _wowzers as default };
+var bar = {
+  foo: function foo() {
+    _foo;
+  },
+  whatever: function whatever() {
+    _whatever;
+  },
+  wowzers: function wowzers() {
+    _wowzers;
+  }
+};